The present invention is related to power transmissions and, more particularly, to a family of power transmissions having three planetary gearsets that are controlled by five torque-transmitting mechanisms to establish at least six forward speed ratios and one reverse speed ratio.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997; U.S. Pat. No. 6,083,135 issued to Baldwin et al. on Jul. 4, 2000, and European Patent Application No. EP 1 033 510 A1 published Jun. 9, 2000.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier and the EP publications each employ three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in each of these publications is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of the present invention to provide an improved family of multi-speed transmissions having three planetary gearsets and five torque-transmitting mechanisms for providing at least six forward speed ratios.
In one aspect of the present invention, the transmission is disposed in a powertrain and has an input shaft driven by an engine and an output shaft driving a final drive mechanism.
In another aspect of the present invention, one of the planetary gearsets has a first member continuously interconnected with the input shaft, a member continuously interconnected with a stationary transmission housing, and a third member which is noncontinuously connected to other transmission members.
In still another aspect of the present invention, the two remaining planetary gearsets have first respective members continuously interconnected and second respective members continuously interconnected.
In yet another aspect of the present invention, the first interconnecting member is continuously connected with the output shaft or selectively connectable with the transmission housing through a stationary torque transmitting mechanism. The second interconnecting member is selectively connectable with either the transmission housing through a stationary torque transmitting mechanism or the non-continuously connected member of the first mentioned planetary gearset, through a rotating torque transmitting mechanism.
In yet another aspect of the present invention, at least one of the two remaining planetary gearsets has a member continuously interconnected with the transmission output shaft and one of the two remaining planetary gearsets has at least one noncontinuously interconnected member.
In yet still another aspect of the present invention, a non-stationary member of the first mentioned planetary gearset is selectively connectible with a member of one of the other planetary gearsets through a selectively engageable torque-transmitting mechanism.
In a further aspect of the present invention, two torque-transmitting mechanisms selectively connect the other non-stationary member of the first mentioned planetary gearset with members of the interconnected planetary gearsets.
In a still further aspect of the present invention, a fourth selectively engageable torque-transmitting mechanism is operable to selectively connect at least one member of the two remaining planetary gearsets with a stationary component, such as the transmission housing.
In yet still a further aspect of the present invention, a fifth torque-transmitting mechanism is selectively engageable to connect at least one member of the remaining two planetary gearsets with a transmission housing member.
In accordance with the object and aspects of the present invention, each family member has three planetary gearsets with each gearset including three members. The first, second or third member of each planetary gearset may be any one of a sun gear member, a ring gear member, or a planet carrier assembly member. The first member of the first planetary gearset is continuously connected with the first member of the second planetary gearset. The second member of the first planetary gearset is continuously connected with the second member of the second planetary gearset. The first member of the third planetary gearset is continuously connected with the input shaft. The second member of the third planetary gearset is continuously connected with a transmission housing. The third member of the third planetary gearset is rotated at a speed proportional to the first member of the third planetary gearset at a speed that may be increased from or reduced from the first member. Therefore the third planetary gearset has a high speed member, a low speed member, and a stationary member.
The first stationary torque-transmitting mechanism connects a member of the first planetary gearset to a transmission housing. The second selectively engageable stationary torque-transmitting mechanism connects a member of the first or second planetary gearset to the transmission housing. The first selectively engageable rotating torque-transmitting mechanism selectively interconnects the low speed member of the third planetary gearset with a member of the first or second planetary gearset. A second selectively engageable rotating torque-transmitting mechanism connects the high speed member of the third planetary gearset with a member of the first or second planetary gearset. The third selectively engageable rotating torque-transmitting mechanism selectively interconnects the high speed member of the third planetary gearset with a member of the first or second planetary gearsets. The input path to the first of the rotating torque-transmitting mechanisms, as described above, is slower than or reduced in speed from the rotational speed of the input path to the second and third rotating torque-transmitting mechanisms.
The five selectively engageable torque-transmitting mechanisms are engaged in combinations of two to establish at least six forward speed ratios and one reverse speed ratio in the planetary gearsets between the input shaft and the output shaft of the transmission.